Electroplating with iron



United States Patent ELECTROPLATIN G WITH IRON John Poor, Portville, N. Y., assignor to Van Der Horst Corporation of America, Olean, N. Y., a corporation of Delaware No Drawing. Application January 16, 1953, Serial No. 331,725

16 Claims. Cl. 204-48 The present invention provides a process for electrodepositing iron. The process is especially adapted to plating iron to build up to desired dimensions, worn or otherwise undersize parts of machines that are subject to severe operating conditions and where accurate dimensioning by machining is required. However it is not limited to such uses as will become apparent hereafter. The base on which the iron is plated may itself be iron, or it may be steel, copper, brass, etc.; generally, apparently, any material that conducts electricity or can be made to conduct electricity.

Many processes and variations of processes for the electrodeposition of iron are to be found in the literature. Of the various earlier processes, those most commonly known now are of course those using electrolytes, or plating baths so called, consisting of aqueous solutions of ferrous sulfate, or of ferrous chloride, or of mixtures of ferrous sulfate and ferrous chloride, with or without various addition agents in each instance. With a ferrous sulfate bath agitation is at least desirable to prevent a nodular form of growth of the deposit and permit a reasonably high rate of production; usually agitation is caused by moving the anode continuously in the bath or rotating the article being plated continuously. Also with a sulfate bath the temperature of the bath, the bath composition and the current density must be controlled carefully and the plates produced by the sulfate baths are not regarded as of as high a quality as those of the chloride baths. On the other hand, the chloride baths must be operated at temperatures approaching that of boiling water. Such high temperatures are a nuisance in a commercial plating shop. Also in commercial plating it is necessary in the majority of cases that parts of the pieces being plated be stopped off, i. e., covered with a protecting material to prevent plating on them, and the materials that are desirable for stopping-01f do not stand well these high temperatures. Further, the chloride baths are quite corrosive and extensive measures are needed to guard the plating tank and accessory apparatus'against their corrosive actions. In addition, neither the sulfate bath nor the chloride bath, nor a bath of a mixture of the two, as these have been known before, is capable of producing, reliably, and day after day under factory conditions, plates that are generally suitable for surfaces that are subject to severe operating conditions. With each of them there is considerable tendency to oxidation of the bath, and considerable insoluble ferric products are formed. Stillfurther, the iron deposited from either a sulfate or a chloride bath, or a mixture of the two, tends to be brittle. Speaking generally, the brittleness can be reduced by subsequent-heat treatment, but the results of the heat treatment are not always uniform, and sometimes at least such high temperatures are required to reduce the brittleness to the desired degree that the hardness of the deposit is reduced. With each of these baths the adherence of the iron plate to the base or foundation on which it is deposited, the bonding as it is called, is too weak and uncertain, when produced under 2,745,806 Patented May 15, 1956 the conditions existing in commercial operations at least", to permit the process to be used where the plate is to be subjected to such high stresses and strains as occur in modern machinery. In general, none of the plating processes heretofore known seem able to produce deposits or plates of iron that are useable generally by industry, or at least to do so commercially.

In contrast with the foregoing, the present process is one that is practical and well adapted for large scale production in commercial plating plants. Further, the plate or deposit of the method or process of the present invention adheres strongly to metal bases (i. e. is well *bonded), and adheres adequately to permit the plate to be used where the stresses are high, except where steps may be taken to prevent strong bonding (e. g. where a plate removable from the base on which it is laid down is desired): means for preventing adhesion or bonding of a plate to the base on which it is laid down are Well known of course. Also the iron plate of this process is dense, tends to be machineable without great difliculty, may be relatively hard or may be relatively soft as desired, and may be brittle or may be relatively ductile as initially laid down (i. e. as plated) depending on the particular form of the process employed, and if too brittle is readily made ductile and tough by heat treatment that does not materially reduce the hardness of the plate. By machineable I mean of course workable by a cutting operation, as on a lathe for example, as distinguished from an abrasive operation such as grinding or honing. Also the plate or deposit of the process is smooth, is substantially free from pits and impurities, has a fine grain structure, and the grain-size need not increase materially with increasing thickness of the plate so that thick plates can be laid down that are substantially homogeneous throughout. Accordingly the deposit or plate of the present process is suitable for substantially any use, including providing machine parts and other articles with surfacings or facings on which machine work must be done, say to bring them to rather exact dimensions, and that are subject to heavy duty, such as, for example, the journal portions of heavy high-speed shafts and the bearings which support such shafts, and members that are subject to severe reciprocating wear conditions, such as the internal walls of engine cylinders.

Further, the operating temperature of the bath may be relatively low. However gentle agitation of the bath by pumping or by some other simple form of agitator may be desirable in some instances in order to maintain the bath properly homogeneous and of uniform temperature throughout, as will be understood from general electroplating practices. Also each of the various factors or elements of the process is operable throughout such a relatively wide range of values, and those which tend to change during plating tend to change so slowly, that the operations are readily controlled.

In the process, iron or steel is used for the anode, at least preferably in order that the anode may feed the bath with iron to more or less completely replace the iron taken from the bath to form the plates. A sludge forms at the anodes, and to avoid this sludge reaching and perhaps contaminating the plate, I usually interpose a porous partition between the anode and the work or article being plated; preferably to this end I-put a porous bag around the anode in which this anode sludge collects; if more than one anode is used, a bag may be provided for each anode or a group of anodes may be enclosed in a single bag.

Iron in ferric form in the bath or electrolyte up to about one and a half (1.5) grams per liter of the bath seems to have little or no deleterious effect; however with concentrations of ferric iron more than about three (3) grams per liter, the deposits tend to be rough, and may certain uses.

appear to have a coarse structure. Where the materials to be used for making up the bath include deleterious metals in substantial quantities, it is best that those materials be purified before being used. However, some foreign metals finding their way into the bath can be removed by exposing the bath to large surfaces of iron metal, such as a quantity of steel wool in a bag suspended in the bath or in a purification column through which the bath is pumped, while electrolysis, ,i. e. working the bath for a time in the same way as plating is done but with dummy cathodes substituted for the work, appears to remove many impurities or foreign metals. Also various organic materials are undesirable in the bath. For example, those organic materials which would tend to buffer the bath and restrain precipitation from it, also tend to cause the inclusion of carbon or carbon compounds in the plates, and this is undesirable in various cases, such for example as when the plating is done to restore work parts of heavy duty machinery to their orig- .inal dimensions. For the most part apparently, organic impurities can be reduced to harmless concentrations by the use of activated carbon. Ordinarily during and throughout the plating operations I circulate the bath or electrolyte through a filter and activated carbon either frequently or continuously to maintain it substantially free of organic impurities and of precipitates, and when a bath has been standing inoperative for a time, before starting plating from it again I usually circulate it through steel wool, activated carbon and a filter to assure the desired purity.

The fiuoborate radical here concerned is, of course, what may be regarded as the radical of borofluoric (tetrafiuoroboric, hydrofiuoboric) acid, HBF4. In a bath or baths or electrolyte of the present composition, the fluoborate content increases the rate of corrosion of the anode during plating over what is would be otherwise and permits errosion to such an extent that the anode or anodes can supply the bath with all the iron necessary to maintain the iron concentration within the desired range. Also within the range of pH at which it is desirable to operate the bath, the fiuoborate restrains the precipitation of iron in ferric form to the degree required for the production of an iron plate that is machineable without great difiiculty and that is suitable for heavy duty. Further, the fluoborate improves the efficiency of material used to reduce ferric compounds to ferrous form, and also tends to prevent rapid clogging of the filters. About the same quantity of fluoborate as appropriately restrains precipitation, is suitable for anode corrosion and for the other services of the fluoborate, and where this is not sufficiently true for practical purposes, an adjustment can be made readily. The fiuoborate radical BF4 content of the present plating bath should not be less than about ten (10) grams per liter of the bath, a already stated above. With very low concentrations of this radical the plates tend to be rough, and with less than about ten (10) grams per liter there is a material tendency for the precipitation of ferric compounds in undesirable quantities and the rate of anode corrosion tends to be too low for This last is especially true when the variables of the bath are correlated to produce a relatively hard plate. On the other hand, with much more than about one hundred (100) grams of this radical per liter of the bath, the dissolution or corrosion rate of the iron anode becomes so high as to tend to be troublesome. Also at the present time it is desirable to keep the fluoborate radical concentration reasonably low for economic reasons. About thirty (30) grams per liter gives adequate protection against ferric compounds and there seems little if anything to be gained by above about fifty (50) grams per liter. About forty-five and four-tenths (45.5) grams per liter is a convenient figure when introducing the radical in the form of ferrous fiuoborate, Fe(BF4)2, and is suitable for both relatively hard and relatively soft plates. Preferably I use ferrous fluoborate as a means for getting the fluoborate radical into the bath since it is a readily obtainable salt, and .is readily soluble in Water, and its cation is not deleterious to either the operations or the plate. The manner in which the radical is obtained in the bath is not a primary essential of the invention however, as will be observed.

The ammonium radical, NH4, in the present bath also acts to restrain the production of iron in the ferric condition through atmospheric oxidation of ferrous iron. More importantly however it also causes the plate to be somewhat harder than it would be otherwise. It also tends to give plates fine grain structures. It is used therefore, speaking generally, when a relatively hard plate is needed but not otherwise. For example, a quite hard plate is desired generally for lining the inner walls of engine cylinders, and in such a case I usually use ammonium radical in the bath. The effect of ammonium radical becomes noticeable at a concentration of about three and one-half (3.5) grams per liter of solution, and speaking generally the higher the concentration the harder the plate. However at concentrations of much more than about thirteen and one-half (13.5) grams per liter of solution, the plate produced tends to be highly stressed in its as-plated condition and there is considerable tendency for it to crack.

The chloride radical, Cl, has several effects. It tends to improve the conductivity of the bath, and thereby permits higher current densities for a given voltage and therewith raises the rate at which the plate can be laid down. It also tends to increase the throwing power of the bath, to reduce the tendency to treeing and a nodular form of growth of the plate, to reduce the grain size of the plate, to the production of a plate that is softer than it would be otherwise, and to the production of plates that are tough and ductile in the as-plated condition or that can be made tough and ductile by heating to temperature too low, or for periods too short, to substantially reduce the hardness of the plate. Were there no chloride radical present in the bath, the plates would tend to be coarse grained, and brittle in the as-plated condition and generally tend to remain permanently brittle unless heated to such temperature and for such periods as would materially reduce the hardness of the plates. When used along with ammonium radical it also tends to relieve the high stresses in the plate and the cracking of the plate which otherwise tend to follow from the ammonium radical, while the ammonium radical tends, contrawise, to offset the tendency of chloride radical to produce a relatively soft plate. The quantity of chloride radical should not, preferably, be much less than six and one-half (6.5) grams per liter of solution, and its effects increase with increasing concentrations of the radical. Thus at a concentration of about ten (10) to fourteen (14) grams per liter of solution and higher, the plates tend noticeably toward a fine grained structure that becomes tough and relatively ductile on heating for a time at, say, about 600 F., and as the concentration is increased above this the ductility of the plate in the aspla'ted condition rises. At concentrations above about twenty-six and six-tenths (26.6) grams per liter of solution, chloride radical enlarges noticeably the range of current densities at which it is possible to produce plates that are not too highly stressed for some purposes even with ammonium radical present up to a concentration of about thirteen and one-half (13.5) grams per liter of solution. At a concentration of about eighty-nine and two-tenths (89.2) grams per liter, with no ammonium and no sulfate radical in the bath (excepting such sulfate as may be introduced as part of a small quantity of a surface active agent), and with the bath maintained at a pH of about three and four-tenths (3.4), the maximum ductility of the plates in the as-plated condition seems to be reached. The maximum possible concentration of chloride radical seems to be limited only by the quantity that can be taken into the bath without introducing an undesired substance (for example, a deleterious cation accompanying the chloride), or producing an undesirably high concentration or an undesirably low concentration of some other desired constituent of the bath (for example, too high a concentration of ammonium radical if the chloride is introduced in the form of ammonium chloride). Accordingly as a practical matter I use usually less than about one hundred (100) grams of chloride radical, C1, per liter of solution.

The sulphate radical, S04, in the reactions of the present baths, when used has a number of effects. E. g. it tends to offset the tendency of chloride radical to make the plate relatively soft, i. e. the sulfate tends to make the plate harder than it would be otherwise. Also sulfate radical tends to increase the conductivity of the bath to a slight extent, and when a large part of the iron of the bath is present as ferrous sulfate, sulfate radical tends to lower the rate of change of the iron to ferric form. Also in coaction with fluoborate radical, sulfate radical tends to raise the secondary anode corrosion rate. However in the present baths its plate-hardening eifect and its effect on anode corrosion are predominant, and both these elfects increase with increasing concentrations of the radical. Primarily it is used for its plate-hardening effect, and speaking generally it can be included in the present baths whenever its plate-hardening effect is needed and in whatever quantities may be needed to obtain or aid in obtaining a desired degree of hardness. However in concentrations of about one hundred and fifty-five (155) grams per liter of the solution, and higher concentrations, it may interfere with the dissolution of iron of the anode to an undesirable extent, especially when the plating operations are continuous for long periods of time. Accordingly I usually limit the concentration of sulfate radical in most cases, when any is used at all, to

a maximum of about one hundred fifty-five (155) grams per liter of solution. Ordinarily when any sulfate radical at all is to be used, in the neighborhood of one hundred and thirty-eight (138) grams per liter of solution is a suitable quantity, all things considered.

Conveniently the iron can be provided in the initial bath in the form of salts (e. g. ferrous fluoborate, ferrous chloride, ferrous sulfate), although this is not necessary. The concentration of the iron in the bath, calculated as the metal, Fe, is not of primary importance. Speaking generally, it may be large or it may be small. From about thirty to about one hundred twenty (120) grams per liter of solution is sufficient.

The sodium lauryl sulfate in the bath reduces the discharge of spray from the bath, and also helps to prevent the formation of pits in the plate. In lieu of or accompanying sodium lauryl sulfate, other sodium salts of the fatty alcohol sulfates, or mixtures of such salts, or other equivalent surface active agents, may be used as before pointed out. Insofar as the effects of such surface active agents may be deemed harmful, or not desirable or unnecessary in any particular instance, none need be used. Very small quantities are sufiicient for the purposes indicated. About one-teenth (0.1) of a gram per liter of solution produces a material effect. There seems to be no top limit to the quantity that can be used, within any reasonable figures, but anything in excess of about twotenths (0.2) gram per liter of solution seems to be unnecessary. Preferably at present I use about one-half (0.5) gram per liter of solution of material now sold on the market under the trademark or trade name Duponol WA Flake.

Speaking generally the higher the temperature of the bath during the plating operations, the higher may be the current density at the cathode, i. e. at the work of article being plated, and accordingly the more rapidly can a plate of a given thickness be produced. Temperatures well about 160 F. can be used, and perhaps temperatures as high as up to boiling may be acceptable for some types of plates, but the higher the temperature the largr tends to be the apparent grain-size of the plate; raising the temperature about 5 F. may cause a perceptible increase in the apparent grain size. Further, the higher the temperature the higher is the rate of evaporation of the bath and the higher the rate of formation of ferric compounds, and above about 155 F. trouble is likely to be experienced with anode bags and with the linings used on the tank walls and on auxiliary apparatus to protectthem against corrosion by the bath. On the other hand, low temperatures, otherthings being the same, tend to the production of plates that are permanently brittle, and to cause cracks in the plate; these cracks may develop during the plating, or not until a considerable time after the plating is finished, and even after a heat treatment of. the plate. Also at F. and lower temperatures, the

current density for the production of plates of high quality is undesirably low. Speaking generally the range of from about 135 F. to about 155 F. is adequate for all purposes, and from about 135 F. to about 145 F. is preferable, all things considered.

The current density at the anode and the current density at the cathode (i. e. the work or article being plated) may differ widely from each other. Further, the current density at the anode can change over a wide range without materially affecting the character of the plate being laid down. This last makes it possible to use an anode continuously or repeatedly unit it has been largely consumed. Speaking generally however the higher the anode current density for a given temperature,- ot'her things remaining the same, the greater becomes the tendencyto polarization at the anode and a high rate of formation of ferric iron, both of which are undesirable effects, and with a bath temperature of about 135 F. an anode current density higher than about one hundred fifty (150) amperes per square foot at least tends to induce excessive polarization at the anode. However, raising the bath temperature permits raising the anode current density for the same effects. For bath temperatures within the range from about 135 F. to about 140 F. and bath pH values ranging from about three and twotenths (3.2) to about four (4) or a little higher, an anode current density of. about one hundred twenty amperes per square foot is quite generally satisfactory. In the opposite direction, apparently there is no low limit for the anode current density so far as the quality and character of the plate is concerned. As to the cathode current density, i. e. the current density at the work or area being plated, the higher the bath temperature the higher may be this current density too, speaking generally, for a plate of a given character. However, the

higher the cathode current density the harder, more brittle and the rougher the plate tends to be and the higher the stresses within the plate. Of course the thinner the plate the less noticeable may be such effects, and the less they need to be considered, regardless of whether such effects arise from the use of a rather high current density, or from the use of a particular radical in the bath, or from a particular concentration of a radical, or otherwise. Thus for example, for a plate one ten-thousandths (.0001) inch thick, with a bath temperature between F. and F., a cathode current density of ninety (90) amperes per square foot may be satisfactory, while a plate one-eighth 4;) inch thick plated under the same conditions but with even a somewhat lower cathode current density, e. g. eighty (80) amperes per square foot, may crack, either during the plating or days later, and heat treating the latter plate at temperatures in the neighborhood of, say, 600 F., even for long periods does not seem to relieve the stresses sufficiently to assure it against cracking subsequently. However a cathode current density of forty ,(40) amperes per square foot with the same bath temperature, is capable of producing plates one-eighth /s) inch thick and more that are tough and ductile after such heat treatment. and otherwise quite satisfactory even for heavy duty service. In brief about one hundred twenty (120) amperes per square foot seem to be about the greatest cathode current density likely to be'desirable, even for the thinnest plates for example, considering also convenience of operation. On the other side, the low limit for the cathode current density, the threshold value for plating as it were, is apparently something of the order of about five amperes per square foot. Of course the lower the cathode current density used the lower will be the rate at which the plate is built up to the thickness it is desired to have. Taking everything into consideration, a cathode current density of about forty (40) amperes per square foot is generally satisfactory for all purposes, and this is the density I now prefer.

Speaking generally, the higher the pH value of the bath the higher is the rate of precipitation of ferric compounds, and the permissible tendency to precipitation of ferric compounds in any instance establishes the maximum permissible pH value of the bath. Ordinarily at least, above a pH of about five (5) the precipitation tends to become excessive. On the other hand, if the pH of the bath is below about two 2), plates laid down by the bath tend to be both brittle and highly stressed, and to remain so under heat treatments at such low temperatures or for such short periods of time that the hardness of the plate is not reduced materially. These considerations establish the permissible range of pH values for the plating bath as from about five (5), and more preferably from about four (4), as a maximum for ordinary plating purposes, to about two (2) although it is conceivable that with a bath temperature as high as the boiling point deposits of a sort may be laid down at a pH of, say, one and eight-tenths (1.8), or possibly down to one and one half (1.5). As a general rule, for comparable results, pH values within the lower portion of the pH range are more suitable when the bath temperatures are high and vice versa, and high cathode current densities are permissible with high bath temperature accompanied by low pH values while a lower cathode current density is required for low bath temperatures accompanied by high pH values. Thus for example, with a bath temperature of about 160 F., a pH of about two and one-half (2.5) and a cathode current density of about forty (40) amperes per square foot, a plate may be produced that has some ductility, at least after a heat treatment of a sort that does not reduce the hardness of the plate materially, while with a bath at room temperature, a pH of from three and onehalf (3.5) to four (4) and a cathode current density even as low as about fifteen amperes per square foot, the resulting plate may be not only hard. but also highly stressed internally and brittle, and

would be more so if a higher cathode current density were used. correspondingly with any chosen bath temperature, the nature of the plate varies with the pH value. Thus for example, with a bath temperature between about 130 F. and 140 F. and a cathode current density of about forty (40) amperes per square foot, a bath pH value above about four and eight-tenths (4.8) tends to cause rather too rapid precipitation of ferric compounds; above a pH of about three and eight-tenths (3.8) or four (4), rather thick plates tend to be rather coarse grained, and the plates may remain brittle after heat treatment at too low a temperature or for too short a time to reduce the hardness of the plate materially; as the pH is reduced below these values the plates become finer grained and harder, and although some may be brittle as-plated these become tough and ductile upon being held at 600 F. for, say, three (3) hours; below about three (3) the cathode metal efficiency tends to fall ott noticeably and the plates tend to be highly stressed internally and brittle, although in some instances a pH as low as two and eight-tenths (2.8) may give a plate that is. brittle as-plated but which becomes tough and ductile with such a heat treatment. All things considered I prefer for ordinary iron-plating purposes bath tempera ture of from about F. to about F., a cathode current density of about forty (40) amperes per square foot, and a pH value of from about three (3) to about three and eight-tenths (3.8). This combination is satisfactory for most purposes in plating iron. For general practice for hard ductile plates that are machineable without great difficulty and plates that otherwise also are well suited for heavy duty service, I use ordinarily (with such a bath temperature and current density) a pH of from three and three-tenths (3.3) to three and seventenths (3.7). Within these ranges, speaking generally, the lower pH values tend to the greater ductility while the higher pH values tend to the greater hardness after heat treatment. With such a bath temperature and current density the softest and most ductile plates in the as-plated condition are obtained from a bath devoid of ammonium radical or sulfate radical (other than such sulfate radical as may be contained in a surface active agent) and having pH value in the neighborhood of three and two-tenths (3.2) to three and one-half (3.5). When a bath is made initially, it may not have a desired pH, or it may depart from the desired pH value during operations. Whenever the pH is lower than desired, either initially or after some plating, the pH may be raised by treating the bath with steel wool for example (e. g. steel wool in a bag can be suspended in the bath until the correction has been made), or by adding, say, ammonium hydroxide, NHiOH, or ferrous carbonate, FeCOa, etc., to the bath. Or the pH can be lowered at any time by adding, say, an appropriate acid, such as sulphuric acid, H2804, or hydrochloric acid, HCl, etc.

It will thus be seen that the iron plates of this process may be relatively soft and ductile, as plated, or may be harder, rather highly stressed internally, and even rather brittle, as plated, depending on the particular radicals and concentrations of the radicals employed in the bath,

'and on the pH value of the bath, the bath temperature during the plating, and the cathode current density selected for the plating operations. Whenever a plate produced within the ranges of these factors particularly indicated above is undesirably brittle or highly stressed, the plate can be made quite tough and ductile and its internal stresses relieved materially by heat treatment. The heating may be to temperatures too low to reduce the hardness of the plate materially even when held at the elevated temperature for a considerable period. Thus holding the plate (or an article on which a plate has been formed) at about six hundred degrees Fahrenheit (600 F.) for two or three hours is satisfactory for substantially all purposes and brings about substantially no reduction in hardness of the plate. Higher temperatures may be used however, and thereby the action speeded up, although temperatures materially higher than six hundred degrees Fahrenheit (600 F.) tend to reduce the hardness of the plate. To an extent at least, this tendency of higher temperatures to reduce the hardness of the plate can be offset by shortening the period at which the plate is held at the higher temperature, and speaking generally, the higher the temperature the shorter need be the period. Thus for example, heating to a temperature of about seven hundred and fifty degrees Fahrenheit (750 F.) for a period of fifteen (15) minutes is about the equivalent in result so far as concerns the plate, to heating to six hundred degrees Fahrenheit (600 F.) for a period of three hours. However if the metal on which the plate is formed is one which absorbs hydrogen during the plating operation, i. e. is subject to hydrogen embrittlement, and especially if the plate is formed on rather massive articles of such metals, the permissible periods of heating to the higher temperatures if the maximum hardness of the plate is to be achieved, may be too short to drive absorbed hydrogen from the article itself, or too short to heat the base article to the proper temperature to drive off its hydrogen, or both. In such instances, heating to the lower temperatures for longer periods, rather than to a higher temperature for a short period, is necessary if embrittlement of the underlying base metal is to be avoided. As before indicated, heating to about six hundred degrees Fahrenheit (600 F.) for about two (2) to three (3) hours is generally sufiicient for most practical purposes. The manner in which the article with its plate is heated is not of primary importance. For example it may be heated in a mufile furnace, or in an air oven through which the air'is circulated. The oven may be heated to the requisite temperature before the plated article is placed in it. After the article has been held at the elevated temperature for the appropriate time, it can be allowed to cool naturally, say at room temperature.

- It may be mentioned also in passing that the fact that both brittleness and internal stresses in plates laid down by the present process can be relieved by temperatures as low as about 600 F. is of some importance in other manners also. Thus in various instances, temperatures much higher than this may have an adverse effect on certain metals that are desirably plated with iron. Again, some devices, e. g. such as some engine cylinders, operate at temperatures somewhat approximating this temperature. In such cases no special heat treatment may be necessary to relieve brittleness and internal stresses in the plate, because the normal use of the device itself will effect the heat treatment.

- An aqueous bath or solution of the radicals indicated can be made up in various ways of course, as will be understood, and the manner in which it is formed is not of primary importance excepting that it is desirable that the fluoborate radical be formed or dissolved in the water of the solution in advance of any other constituent of the bath other than, say, such ferrous iron as may accompany the fluoborate radical as a cation. By thus giving it precedence, the fluoborate radical prevents the formation of insoluble or diificultly soluble ferric compounds that may be formed otherwise. Preferably however, I form the bath from salts of the radicals that are to compose it, e. g. of such quantities of ferrous fluoborate,.ferrous and/or ammonium chloride, and ferrous and/or ammonium sulfate, as may be necessary to yield the bath desiredin a particular instance, since these salts are readily available and dissolve quite readily in.water. Ordinarily when the bath is made up of such salts at least,- it best be purified before use, and preferably the bath is made up in a tank other than the plating tank in order to keep the plating tank free of the purifying material and possible precipitates and contaminants of the materials used in making the bath. The bath may be made up and purified in the following manner: First, take about one-half /2) the required quantity of water heated to, say, between 120 F. and 150 F., in order to hasten the dissolution of the salts, and in this dissolve the quantity of ferrous fluoborate Fe(BF4)2, needed to furnish the bath with the selected quantity of fluoborate radical. After this is dissolved or substantially so, add to this solution whatever sulfate or sulfates and chloride or chlorides that may be needed to provide the final plating bath with the remainder of those radicals and those concentrations of them that are desired for the bath in the particular instance. Then add sutficient water, also preferably heated to, say, 120 F., or 150 F., to bring up the volume of this incipient solution to seventyfive per. cent (75%) or more of the volume the final plating bath is to have; the incipient solution may be stirred gently (i. e. without aeration) to complete and hasten the dissolution of the salts. When all the salts have been dissolved, add sufi'icient steel wool (say No. 3 or No. 4 steel wool) to the solution to raise the pH of the solution to about four (4) or higher. Usually from five (5) to ten grams per liter of the solution is sufiicient. The purpose of adding the steel wool is to precipitate various impurities that may have accompanied the make-up salts, to reduce to the ferrous condition ferric iron that may be'present, and to neutralize acid usually contained in the make-up salts. The reaction with the steel wool can be hastened by holding the solution at an elevated temperature, say at from 120 F., to 150 F.; with a temperature of 130 F. or higher, usually the reaction will be completed overnight. Considerable gassing and a tendency to spray tiny droplets of the solution into the atmosphere accompanies this reaction; to suppress the spray the make-up tank can be covered, or a small quantity of one or more of the surface active agents mentioned above can be added, say about four one-hundredths (.04) gram per liter of the solution. When the pH of the solution has risen to four (4) or higher, add to the solution from three (3) to five (5) grams per liter of activated carbon and a like quantity of cellulose filter-aid, and stir the solution gently periodically or continuously to-keep the carbon and filter-aid suspended in the solution until impurities accompanying the make-up materials, as these are available on the market usually, are absorbed. This may take three (3) hours or longer. In addition to helping to purify the bath, this treatment with activated carbon removes almost completely any surface-active agent that may have been added to suppress spraying. After these treatments have been completed, run the solution through a filter to remove the undissolved matter in it. Then take the quantity of surface-active agent it is desired the bath should contain, dissolve it in a small quantity of hot water, and add this solution to the filtered solution. Then add sufficient water to bring upthe whole to the volume the plating bath is to have, and thoroughly mix the whole. Then add concentrated sulphuric acid, H2804, as may be necessary to lower the pH of the bath to the desired value, for example, to within the range from three and threetenths (3.3) to'three and seven-tenths (3.7). The bath is then ready to operate. However a few hours of operation or pre-plating electrolysis may improve its performance. It may be noticed that the stirring referred to above, as well as all other stirring or other agitation to which a finished bath may be subjected, is best gentle, i. e. carried on in such a manner as not, ordinarily, to disturb any more than possible any deleterious precipitates that may fall to the bottom of the plating tank, or carry air into the bath because air in the bath promotes the formation of ferric compounds.

If a bath is allowed at any time to stand for any considerable period without plating being done in it, it is well,'before plating is started or resumed, to circulate it for a little time through steel Wool, activated carbon and a filter to remove deleterious substances that may have formed in it. In addition, in maintaining a bath in good operating condition, it is well, as before indicated, that it v be filtered and purified either at frequent intervals or continuously during the plating cycles. This can be done by circulating the bath at intervals or continuously during plating through activated carbon and a filter. Water is added from time to time as necessary to maintain the volume of the bath. Under the operating conditions particularly recommended however, there is little loss of the radicals in plating, other than mechanical losses, i. e. such as are due to leakage, to drag-out (which is carrying away in solution clinging to the plated articles when theseare taken from the bath), etc. As the concentrations of radicals fall unduly for such or other reasons the bath can be replenished with them. Thus as the concentration of fluoborate radical falls, e. g. as it comes toward about thirty (30) grams per liter of the bath, ferrous fluoborate may be added to bring its concentration back to a higher figure; or if the pH of the bath happens to be higher than necessary, fluoboric, HBF4, acid can be-added instead. A deficiency of sulfate radical can be made up by adding ferrous sulfate for example, or should the ferrous sulfate concentration become objectionably high, it can be reduced in manners already pointed out. When ferrous sulfate is crystallized out however, ammonium radical, if there is any in the bath, may be lost with it. Reduction of ammonium radical concentration lost in this way or otherwise can be made up by, say, the addition of ammonium chloride to the bath. Loss of chloride radical can be made up by the addition of, say, ferrous chloride, or more or less made up by the addition of ammonium chloride if the bath is one containing ammonium radical. The pH value of the bath tends to change usually during plating, the direction and rate of change being dependent on various factors, such as the relative sizes of the anode and the cathode, and the anode polarization. As it may rise too high, it can be lowered by, for example, adding sulphuric acid to the bath; as it may fall too low, the pH can be raised by, for example, treating the bath with steel Wool; for example, by suspending a mass of steel wool in a porous bag in the bath. The pH value of a bath can well be determined and corrected at least daily; While ferric iron tends to form from atmospheric oxidation, on the other hand the plating operations may reduce ferric iron to the ferrous condition; and accordingly in a given bath the ferric iron concentration may tend to reach a certain fixed value. As its value may become too high, it can be reduced by treating the bath with steel wool; for example, in the manner described above for correcting pH value. At least until its net rate of formation and an equilibrium concentration have been determined in a particular bath and under the particular conditions of operating that bath, and an appropriate periodic or continuous correction applied, the ferric iron concentration can well be determined every few days and correction made as frequently. Assuming that the baths are constituted and operated as prescribed above, little or no attention need be paid to the concentration of iron, as metal, in them, and with the attention indicated above they willoperate for indefinitely long periods.

As an example of the foregoing, assume that a plate that is relatively soft and that is noticeably ductile as plated is desired. A good bath for such a plate may consist of the following ingredients in the quantities stated per liter of solution by volume: fluoborate radical calculated as BF4, about forty-five and four-tenths (45.4) grams; chloride radical, Cl, about eighty-nine and twotenths (89.2) grams; iron, Fe, about eighty-four and nine-tenths (84.9) grams; sodium lauryl sulfate or equivalent, about two-tenths (0.2) gram; water sufficient to make one liter of solution by volume. To obtain substantially this bath take the following materials in the quantities stated per liter of the bath: ferrous fluoborate, Fe (BFUz, sixty (60) grams: ferrous chloride, FeCl2-4H2O, two hundred fifty (250) grams; and a sodium lauryl sulphate containing compound such as Duponal WA Flake, one-half (0.5) gram; sulficient Water to make up one liter by volume. Make up the bath from these materials in the manner described above, purifyingin the manner described above, and then as necessary add sutficient hydrochloric acid to reduce the pH value to between three and two-tenths (3.2) and three and five-tenths (3.5); for maximum ductility as-plated,"

reduce the pH. to about three and four-tenths (3.4). In a plating tank, maintain the bath at a temperature of between 135 F. and 140 F., say by means of an immersion heater in the tank. For the anode in the bath, use the low carbon steel known as SAE 1020; use such a size of anode or anodes, relative to the size of the area to be plated, that with a cathode current density. of forty (40) amperes per square foot the current density at the anode will be less than about one hundred twenty (120) amperes per square foot; put a porous bag around the anode, or at least so much of it as is to be immersed and active in the tank, as described above. Clean at least that part of the article which is to be immersed in the plating bath to remove, dirt, oil, scale, etc. Immediately after cleaning rinse the article thoroughly with mersed in the bath. Accordingly either immediately afterimmersion of the article orafter some such delay, apply direct current to the anode and the article to be plated, the connections being such that the article is the cathode. Also it may be helpful to start with alow current density as before pointed out, i. e. use such a current initially that the cathode current density is about ten (10) amperes per square foot, and continue this for, say, ten (10) minutes. With or without such an initial low current, apply such current that the current density at the article is about forty (40) amperes per square foot and continue this until a plate of the desired thickness has been obtained. If the bath is to be. used fora time, on the same or a succession of articles, filter and purify it frequently or continuously during the plating; also replenish the bath constituents and correct the pH value as may be necessary to bring the concentrations and pH .back to about their initial values occasionally as will be understood from theforegoing; also replenish the bath with water as may be needed to maintain the volume of the bath. When the desired thickness of plate has been obtained on an article (this can be determined suificiently closely by noting the length of time the plating is continued, as will be understood from prior plating practices), remove the article from the bath, and rinse it with water. If the plate is not then as :tough and ductile as desired, heat the article in an air oven to about 600 F. and hold it at this temperature for three (3) hours or longer. After this heat treatment the article can be removed from the oven and allowed to stand at room temperature until cool. H I

As a further example, assume that a relatively hard plate is desired, e. g. a plate suited for the inner walls of engine cylinders. A suitable bath for such a plate is one consisting of the following ingredients in the quantities stated per liter of solution by volume: fiuoborate.

radical calculated as BF4, about forty-five and fourtenths-(45.4) grams; ammonium radical, NH4, about six and three quarters (6.75) grams; chloride radical, Cl, about thirteen and one-quarter (13.25) grams, sulfate radical, S04, about one hundred thirty-eight and twotenths (138.2) grams; iron, Fe, about ninety-four and nine-tenths (94.9) grams; sodium lauryl sulfate or equivalent, about two-tenths (0.2) gram; water sufiicient to make one (1) liter of solution by volume. To obtain substantially this bath take the following materials in the quantities stated per liter of the bath: ferrous fluoborate, Fe (BF4)2, sixty (60) grams; ferrous sulfate, FeSO4-7H2O, four hundred (400) grams; ammonium chloride, NH4C1, twenty (20) grams; Duponal WA Flake, one-half (0.5) gram; sufiicient water to make up one liter by volume. Use the same procedure for making up, purifying and replenishing the bath, and for cleaning and plating the article, etc., as in the preceding example, except establish and maintain the pH value of the bath within the range of from about three and three-tenths (3.3) to about three and seven-tenths (3.7). In a plating tank maintain the bath at a temperature between F. and F. Use an anode of the same steel as in the preceding example, and the same size of anode relative to the size of the area to be plated. With or without the delay in applying the current, and the low initial current density described above, plate at a cathode current density of forty (40) amperes per square foot. After the plating is finished, rinse the article with water and give it the heat treatment described in that preceding example, or omit the heat treatment as the situation may dictate.

The use of fractions in the formulae of radicals above is not to be understood as indicating that the concentrations are highly critical in any particular instance; for the most part the use of fractions in these formulae arises from my preference to use salts in the making up of the baths and my desire to use convenient round number quantifies of those salts as will be seen from the examples given above; the concentrations in terms of radicals and the metal iron can be varied noticeably in any particular instance as will he understood from the discussions of radicals and the iron content above.

In general it will be understood that the invention is not limited to the specific details mentioned above except as appears hereafter in the claims.

I claim:

1. A process for electrodepositing iron which comprises electrolyzing an aqueous acid solution consisting essentially of ferrous iron, not more than 3 grams per liter of ferric iron, and at least 26 grams per liter of acid radical selected from the group consisting of chloride radical and a combination of chloride and sulphate radicals, in such combination the chloride radical being present in the amount of from 6 /2 to 100 grams per liter, and from to 100 grams per liter of fluoborate radical.

2. A process for electrodepositing iron which comprises electrolyzing an aqueous acid solution consisting essentially of ferrous iron, not more than 3 grams per liter of ferric iron, and at least 26.6 grams per liter chloride radical, and from 10 to 100 grams per liter of fiuoborate radical.

3. The process as defined in claim 1 wherein the solution also contains between 3 /2 and 13 /2 grams of ammonium radical per liter of solution.

4. The process as defined in claim 2 wherein the solution also contains between 3 /2 and 13% grams of ammonium radical per liter of solution.

5. The process as defined in claim 1 wherein the solution is maintained substantially between room temperature and 160 F.

6. The process as defined in claim 2 wherein the solution is maintained substantially between room temperature and 160 F.

7. The process as defined in claim 1 wherein the electrolyzing potential is adjusted to maintain a current density at the anode of less than 150 amperes per square foot.

8. The process as defined in claim 2 wherein the electrolyzing potential is adjusted to maintain a current density at the anode of less than 150 amperes per square foot.

9. The process as defined in claim 7 wherein the current density at the area being plated is substantially maintained at less than 100 amperes per square foot.

10. The process as defined in claim 8 wherein the current density at the area being plated is substantially maintained at less than 100 amperes per square foot.

11. The process as defined in claim 1 wherein the solution is maintained at a pH value between 2 and 5.

12. The process as defined in claim 2 wherein the solution is maintained at a pH value between 2 and 5.

13. A plating bath for the electrodepositing of iron consisting essentially of an aqueous solution containing per liter of solution about 45 grams of fluoborate radical, about 89 grams of chloride radical, about grams of ferrous iron, not more than 3 grams of ferric iron, and about .2 gram of sodium lauryl sulfate, and water sufiicient to make 1 liter by volume.

14. A plating bath for the electrodepositing of iron consisting essentially of an aqueous solution containing per liter of solution about 45 grams of fluoborate radical, about 6.75 grams of ammonium radical, about 13.25 grams of chloride radical, about 138 grams of sulfate radical, about grams of ferrous iron, not more than 3 grams of ferric iron, about .2 gram of sodium lauryl sulfate, and water suflficient to make 1 liter of solution by volume.

15. The process of electrodepositing iron comprising electrolyzing an aqueous acid solution as defined in claim 13, wherein the temperature of the solution is substan tially maintained between 135 F. and 150 F., the pH value of the solution being maintained between 3 and 4, the current density at the area being plated being maintained at about 40 amperes per square foot, and the current density at the anode being maintained at less than amperes per square foot.

16. The process for electrodepositing iron comprising electrolyzing an aqueous acid solution as defined in claim 14, wherein the temperature of the solution is substantially maintained between F. and F., the pH value of the solution being maintained between 3 and 4, the current density at the area being plated being maintained at about 40 amperes per square foot, and the current density at the anode being maintained at less than 100 amperes per square foot.

References Cited in the file of this patent UNITED STATES PATENTS 1,516,326 Bouchayer Nov. 18, 1924 1,562,710 Madsen Nov. 24, 1925 1,567,625 Smith Dec. 29, 1925 1,607,960 Madsen Nov. 23, 1926 1,645,927 Pierce Oct. 18, 1927 1,780,213 Vertucci Nov. 4, 1930 1,862,745 Fuller et a1 June 14, 1932 1,912,430 Cain June 6, 1933 1,937,068 Pawlek Nov. 28, 1933 2,092,130 Lyons Sept. 7, 1937 2,304,709 Rubin Dec. 8, 1942 2,359,224 Knol Sept. 26, 1944 2,420,403 Stoddard May 13, 1947 2,465,747 Pessel Mar. 29, 1949 2,523,160 Struyk et a1 Sept. 19, 1950 2,580,681 Konrod et a1 Jan. 1, 1952 FOREIGN PATENTS 154,282 Great Britain Nov. 8, 1920 

1. A PROCESS FOR ELECTRODEPOSITING IRON WHICH COMPRISES ELECTROLYZING AN AQUEOUS ACID SOLUTION CONSISTING ESSENTIALLY OF FERROUS IRON, NOT MORE THAN 3 GRAMS PER LITER OF FERRIC IRON, AND AT LEAST 26 GRAMS PER LITER OF ACID RADICAL SELECTED FROM THE GROUP CONSISTING OF CHLORIDE RADICAL AND A COMBINATION OF CHLORIDE AND SULPHATE RADICALS, IN SUCH COMBINATION THE CHLORIDE RADICAL BEING PRESENT IN THE AMOUNT OF FROM 61/2 TO 100 GRAMS PER LITER, AND FROM 10 TO 100 GRAMS PER LITER OF FLUROBORATE RADICAL. 